Growth, feed and nutrient utilisation and gastrointestinal evacuation time in Atlantic salmon ( Salmo salar L.): the effect of dietary fish meal particle size and protein concentration

Growth, nutrient utilisation and gastrointestinal evacuation time using different fish meal particle sizes and dietary protein concentration was examined in Atlantic salmon. Salmon were given micro, standard or coarse grounded fish meals at two dietary protein concentrations (30 or 45%) in isolipid diets. Gastric evacuation time was influenced by fish meal particle size. Coarse ground fish meal gave a slower gastric evacuation time compared to finer ground fish meal. Specific growth rate was not influenced by the protein concentration, but there was an adverse effect of coarse ground particles. This effect may be explained by the reduced feed intake of fish fed diets containing coarse ground fish meal. Feed conversion ratio (FCR) or energy conversion ratio (ECR) was reduced with increasing dietary protein concentration. This effect was mainly caused by different energy levels in the diets and not protein/carbohydrate levels. Standard coarse fish meal gave a reduction in ECR, but there was no effect of fish meal particle size on FCR. A protein sparing effect of starch was demonstrated. Productive protein value (PPV) and productive energy value (PEV) was not affected by dietary protein concentration or fish meal particle size. Dietary protein concentration had no effect on nitrogen or fat digestibility but there was a reduction in fat digestibility when coarse ground fishmeal was used in the diets. There were only minor effects on the dressing out percentage, condition factor and fat in cutlet.